Add Contributing File

[bhavesh1129]

Hey @Harshit564!
I had checkout your project and it is so good but as I can see you haven't added anything in your contributing.md file so I want to take up this issue and make your contributing.md file awesome as your project is.

Thank you!

[Harshit564]

Yeah sure! Go ahead.

[bhavesh1129]

Also, it would be very kind of you if you add the label of level type.